Not Applicable
Not Applicable
This invention relates to a rotary compression press for cylindrical compacts, especially tablets.
From DE-GM 88 16 064, a rotary compression press of the generic type is known in which the shank of the pressing rams has a tooth system which cooperates with a stationarily disposed rack. The rotational motion of the upper and lower rams immediately after the pressing operation and during the withdrawal of the ram from the die is intended to achieve separation from the surface of the tablet which has been pressed. In the case of particularly adhesive materials being compressed adherence must be feared between the rams and the material if there is no rotation. The drawback of the known press is that if the tooth systems of the upper and lower rams engage the rack jammings might occur, depending on the position in which the respective upper and lower rams have stopped after exiting from the rack concerned. Another drawback is that the rams will rotate only after passing the pressure rollers. This does not prevent the pressed compacts from adhering to the rams already before a rotation is performed.
From EP 0 448 190, a rotary compression press has become known in which the upper and lower rams are guided in bushings which, in turn, are pivotably supported and are toothed in order to cooperate with a stationary tooth system. The shanks of the rams are guided in the bushings in a linear manner. The drawback of this relatively expensive assembly is that the rams will rotate even under a maximum pressing power. This, however, will result in significant wear and also may have an adverse effect on the material compression which is desired. In order to reduce wear to the pressure rollers and the heads of the rams facing them it also has become known already to design the rams in two parts and to make them rotatable with respect to each other. While this will save the head of the ram it will cause considerable stress to act upon the bearings between the ram parts. Moreover, such bearings are exceptionally expensive.
It is the object of the invention to provide a rotary compression press wherein the rotational motion of the pressing rams is produced by simple means and significant wear is avoided at the same time.
In the inventive rotary compression press, the opposed tooth system is defined by a rotatably supported gear which is acted on by a preset braking torque. The braking torque has been chosen so as to be smaller than the torque of the ram when under a maximum pressing power.
The invention is based on the finding that although it is desirable to effect a rotation of the rams when a pressing power is still exerted thereon this need by no means be the maximum pressing power. Rather, it will be sufficient for a rotation to be effected only when the pressing power has reached a relatively low value. In such a case, this rotation will no longer have an adverse effect on the head of the ram and the pressure roller. According to the invention, this will be achieved by the action of a certain braking torque on the gear, which causes the gear to rotate along if the braking torque is smaller than the torque required to rotate the ram. Therefore, if pressing powers are more or less large, especially if the pressing power is a maximum, the ram will not rotate even if the tooth system of the ram is in engagement with the gear. Not until the torque falls below the braking torque on the ram the gear will stop and the ram will then undergo a rotation. Although the rotation thus caused will take place only along a short distance of travel of the ram and, hence, will only lead to a rotation at a small angle it will be completely sufficient to avoid adherence of the material to the ram and to bring about the release of material which adheres thereto.
The braking torque is tailored so as to effect a rotation of the pressing ram only if the pressing power is such as to produce a torque which is merely a fraction of the maximum pressing power.
Since it cannot be ensured that the tooth systems engage each other completely from the very beginning, but the teeth may happen to stand upon one another initially, the spring assembly, in an aspect of the invention, provides that the gear may be compliant until the tooth systems fully slide into engagement. It is understood that the bearing component abuts against a stop on the side opposed to the spring assembly in order to give the gear a proper initial position for engagement of the ram with the gear.
Various constructional options are imaginable to cause a braking moment to act upon the gear. According to the invention, one of them is that the gear has at least one of its front-end face fitted with a friction surface which cooperates with an opposite friction surface each. Preferably, the friction surfaces are pressed against one another by a spring assembly. In another aspect of the invention, the spring assembly may be formed by a pack of disk springs. The bias of the braking spring is preferably variable to make a desired braking torque adjustable.